“I cannot and will not support my party's nominee for president regardless of the political impact on my candidacy or the Republican Party,” the embattled senator said in a statement.

“After much consideration, I have concluded that Donald Trump has not demonstrated the temperament necessary to assume the greatest office in the world,” Kirk said. “I have spent my life building bridges and tearing down barriers—not building walls. That's why I find Donald Trump's belief that an American-born judge of Mexican descent is incapable of fairly presiding over his case is not only dead wrong, it is un-American.”

Only this morning, Kirk's campaign had been unwilling to go that far, despite criticism by Kirk last year. But Trump's refusal to back down was becoming a rising issue.

The statement stops short of saying who, if anyone, Kirk now will endorse, but a CNN reporter tweeted:

.@SenatorKirk tells @mkraju he won't vote for Hillary and plans to write in Gen Petraeus for president

Kirk foe Tammy Duckworth issued a statement after the move. “What took so long? Apparently for Mark Kirk, it's acceptable to refer to Mexicans as rapists; to propose banning Muslims from entering the country; to call women fat pigs and dogs; to mock a reporter's disability; and to insult just about everyone who doesn't look like Donald Trump. Until today, and for nearly a year, Kirk was fine with all of that, and even saw a 'net benefit' in Trump's campaign, and offered himself up as a potential adviser.”

And Gov. Bruce Rauner finally jumped into the fray, echoing Kirk's comments after days of silence.

From a statement: "I am disgusted by these recent comments, and as I've said many times, I'm appalled by the rhetoric in the presidential race. Those comments do not reflect the values of the Republican Party. They do not reflect the values of America."

Rauner's statement potentially is of major significance, if it means the governor will deny Trump aid and support from the Illinois Republican Party.

Update, 7:30 p.m.

Still no slashing Trump tweet about Kirk. At least for the moment, Trump seems to be trying to calm the furor some, releasing a statement saying that, while he thinks he's been treated unfairly, his comments about the judge have been “misconstrued” and “I do not feel one's heritage makes them incapable of being impartial.”

But the damage is done.

Earlier:

Donald Trump's continuing declarations about "Mexican" judges and the like have U.S. Sen. Mark Kirk, R-Ill., caught in a classic political dilemma—one he may not escape without considerable damage.

Much as Kirk would rather talk about Duckworth's upcoming whistleblower trial, Trump's refusal to back off statements about Judge Gonzalo Curiel that many consider outright racist is beginning to overwhelm other news in the tight race. Trump has been hammering at Curiel, an Indiana native, as conflicted and unfit to oversee a Trump University class action lawsuit because of the judge's Mexican heritage and the presumptive Republican presidential nominee's promises to build a wall on the U.S.-Mexican border.

Illinois Democrats are pouncing with claws out, ripping Kirk at an Emily's List event yesterday and today putting up a website that compares past Kirk comments of note—like his quip that a single colleague was "a bro with no ho"—with Trump's statements that he can't get a fair legal shake from a judge of Mexican ancestry or, theoretically, one who practices the Muslim faith.

In fact, Kirk has been critical of Trump, a year ago telling him to "shut up"—in Spanish no less. But Kirk also has said he'll support the presidential nominee of the Republican Party, leaving himself open to attack.

If Kirk follows the lead of some other GOP senators and rips Trump again, he risks losing the support of Trump backers in Illinois. And there are a lot of them—Trump got more votes than any other candidate in the March Republican primary. But if that criticism stops short of retracting his endorsement, Kirk will look like he's trying to have it both ways.

So far, all Kirk campaign manager Kevin Artl is saying is that the senator "has continually criticized Trump over his comments about Latinos. . . .He has continually outlined the areas of disagreement he has with Trump."

Artl also asks if Duckworth "will testify" in that upcoming trial and not just stick with the deposition she's filed denying any misconduct when she was head of the Illinois Department of Veterans Affairs.

Team Duckworth isn't answering that question right now. Its comment, from spokesman Matt McGrath: “Tammy has complied at every step of this process, even as the civil case has stretched out over eight years and been dismissed in full or part three different times. The Kirk campaign, meanwhile, has made it clear they have nothing more to offer Illinois families and are going all-in on their bogus version of this case."

So it goes. As long as Trump continues to dominate the headlines with wild statements, Duckworth forces will be able to pretty much avoid the subject.